Field of the Invention
The present invention relates to a wafer dividing method for diving, along plural streets (planned dividing lines), a wafer on which these plural streets are formed in a lattice manner on the front surface and devices are formed in plural regions marked out by the plural streets.
Description of the Related Art
In a semiconductor device manufacturing processing, plural regions are marked out by planned dividing lines that are arranged in a lattice manner on the front surface of a semiconductor wafer having a substantially circular disc shape and are called streets, and devices such as integrated circuits (ICs) and large scale integrations (LSIs) are formed in these marked-out regions. Then, the wafer is cut along the streets to divide the regions in which the devices are formed and manufacture the individual device chips.
As a method for dividing along the streets of the above-described wafer, a laser processing method is also attempted in which a pulse laser beam having such a wavelength as to be transmitted through the wafer is used and the wafer is irradiated with the pulse laser beam, with the light focus point set inside the region along which the dividing should be performed.
One example of the dividing method using this laser processing method will be described more specifically. A protective member is disposed on the wafer front surface on which devices are formed, and the wafer is irradiated with the laser beam having such a wavelength as to be transmitted through the wafer from the back surface of the wafer, with the light focus point positioned at the inside of the wafer corresponding to the planned dividing line, to form modified layers along the planned dividing lines. Thereafter, the side of the protective member disposed on the front surface of the wafer is held by a holding unit and the back surface of the wafer is ground by a grinding unit to process the wafer to a target finished thickness. By this processing, the modified layers are removed and the wafer is divided into the individual device chips along the planned dividing lines (for example, refer to Japanese Patent No. 3762409). According to this dividing step, cracks are formed when the modified layers are formed. Thereafter, by carrying out the grinding by the grinding unit, the wafer is divided into the individual device chips, with these cracks serving as the origin of the dividing. Thus, the wafer can be efficiently divided without the need to take a measure such as additionally applying an external force.